Apparatus for compacting a paper web



Dec. 6, 1966 c. B. A. IHRMAN 3,290,209

APPARATUS FOR COMPACTING A PAPER WEB Filed July 16, 1964 United States Patent Sweden 7 I Filed July 16, 1964, Ser. No. 383,170 1 Claim. (Cl. 162-361) The present invention relates to an improved device for making paper extensible by creping or shrinking the same while in a moist state.

Creping by means of rolls is known before, e. g. from the Austrian Patent No. 79,413 (Lemberger) or the French Patent No. 1,248,905 (Erspamer). Creping by means of a resilient blanket is known from the Swedish Patents Nos. 128,209 (Grettve) and 149,162 (Clue-ft). In either case a moist and plastic paper 'web is passed through a pressure nip together with a layer of a soft elastic material, such as rubber. In the pressure nip one side of the paper web rests against the rubber layer and the other side is applied against the hard surface of a roll, e.g. of steel. The rubber layer is compressed in the pressure nip and is correspondingly extended in the running direction of paper web, and therefore it contracts where it departs from the pressure nip, the paper web being creped or shrunk where it adheres to the surface of the rubber layer. However, the shrinkage can start only after the pressure of the paper web against the steel roll has decreased enough to allow the web to slide relatively thereto, i.e. after the friction of rest has been overcome, the shrinkage starting the earlier the lower the friction of rest is. Therefore, a low specific friction of rest enables the application of a high nip pressure favourable with regard to certain desired paper qualities. Among others, a visible crinkling is prevented by a high nip pressure, and a high resistance to extension during the drying of the web is obtained thereby.

Thus a low value of the friction of rest is desirable during the shrinking operation. This is usually obtained by heating the steel roll, but it has also been suggested for said purpose that the roll be given a highly polished or even chromium-plated surface. In spite thereof it happens that the friction becomes so high that a lubricant, usually a silicon oil, has to be used which involves complications.

According to the present invention the friction prob lem is solved in a new manner by using a device characterised in that the surface of the hard roll is made with equidistant grooves extending substantially in the running direction of the web. The device and the results obtained thereby will be more closely described with reference to the accompanying drawing, in which FIG. 1 diagrammatically shows a cross-section of a device for creping paper by means of rolls, FIG. 2 shows a corresponding cross-section of a device for creping paper by means of a resilient blanket, and FIG. 3 is an enlarged longitudinal vertical cross-sectional view illustrating a portion of the pressure nip of the device shown in FIG. 1 or 2.

In FIG. 1, the numeral 11 designates a paper web having a moisture content of 20 to 40 percent, which is drawn through a pressure nip formed between two cylindrical rolls 13 and 15, the rolls 13 being covered with an elastic surface layer 17, preferably of rubber, whereas the roll 15 which preferably is made of steel and heated, is made with a hard surface. The rolls are pressed together with a line pressure of 15 to 25 kilograms pro centimeter, and

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the hard roll 15 is driven with a peripheral speed which is 6 to 15 percent greater than the peripheral speed of the roll 13 having the elastic surface layer. In the pressure nip the paper web is subjected to a shrinkage or compaction in its longitudinal direction, which is fixed by a subsequent drying operation and which gives the paper an increased extensibility.

The steel roll 15 was turned in a lathe and a finishing cut was taken having a pitch of 3 turns per millimeter axial length, whereby the roll was given an essentially saw-toothed profile and showed equidistant grooves 19 (FIG. 3) running essentially in the peripheral direction and having a depth of about 0.1 millimeter, and the grooves were spaced about grooves per inch of the axial length of the surface of the steel roll 15.

A paper web shrunk by the use of the above-described device and dried was compared with a paper web that had been shrunk by a similar device having a finely polished steel roll 15, the remaining conditions being the same. In the former case an improvement of the longitudinal extensibility of the paper from 4.25 to 6.25 percent was obtained and simultaneously the shrinking operation took place with a better stability and could be controlled in a more efficient manner.

In the above-described trial the roll was initially smooth, but rust appeared on the surface after some time of use. Said rust proved to have a favourable influence upon the shrinking or compacting operation on account of a further decrease of the friction, which may be at tributed to the lubricating effect of the iron hydrate as well as to the etching of the surface.

The roll with the above-mentioned depth of the grooves made "by the finishing cut gave rise to a slight embossmcnt of the paper web, differing merely slightly from the marks obtained during the forming of the web upon the wire. However, the rubber surface should not be so soft that the grooves are completely filled out by the paper, which would unduly increase the friction, but the paper ought to slide mainly against the ridges between the grooves. During the prevailing conditions a hardness of the rubber of 50 Shore or more proved to give excellent results.

In certain cases the embossment of the paper surface may be undesirable. Then it is possible to eliminate the same by smooth-pressing the web before the drying thereof, which further improves the strength of the paper. In other cases the embossment may be desired. Some pasting or laminating trials have shown, e.g. that a hard-sized paper into which the adhesive penetrates only with great difficulty, gives a better adhesion when the surface is embossed as described above.

In the device shown in FIG. 2, the elastic layer 17 takes the shape of an endless blanket extended between the rolls 13 and 18. The device is the same as that shown in the US. Patent No. 2,624,245. However, as regards the hardness of the surface of the rubber layer 17 and the rough surface structure of the steel roll 15, the device of FIG. 2 corresponds to the device shown in FIGS. 1 and 3.

Of course, the invention is not restricted to the abovedescribed embodiments, but may be modified in various respects within the scope of the following claims. Thus for instance, the shrinking operation may take place without heating the hard roll, and the low friction of the latter may also be had by a different grooving thereof than that described above.

I claim:

In a device for compacting a web of paper wherein the device includes a pressure nip in which the 'web of 3 4 paper is supported by an elastic surface layer which presses ridges to prevent the paper web from being pressed the web against the surface of a hard roll while the web down into the grooves. fi g ggf i gglg s gt Surface of the hard roll the 1m References Cited by the Examiner equidistant grooves circumferentially around the sur- 5 UNITED STATES PATENTS face of said hard roll for reducing friction between the hard roll surface and the web of paper which is y at alu sliding on said surface, said grooves being formed in 51 5 6/1959 X5 X the running direction Of the Web Of paper and being Screeton et .a1 of such configuration that equidistant ridges are 10 3104197 9/1963 Back et a] X formed on the hard roll surface between each of n the grooves, said grooves at a spacing of about 75 FOREIGN PATENTS grooves per inch of the axial length of the surface of 1,248,905 11/1950 F the hard roll, said elastic layer having a Shore durometer hardness 15 DONALL SYLVESTER P'lmmy Exammer' of at least 50", which layer cooperates with said S. LEON BASHORE, Examiner. 

